Radiation diffractive materials based on crystalline colloidal arrays have been used for a variety of purposes. A crystalline colloidal array (CCA) is a three-dimensional ordered array of mono-dispersed colloidal particles.
Such colloidal dispersions of particles can form crystalline structures having lattice spacings that are comparable to the wavelength of ultraviolet, visible or infrared radiation. These crystalline structures have been used for filtering narrow bands of selected wavelengths from a broad spectrum of incident radiation, while permitting the transmission of adjacent wavelengths of radiation. Prior devices have been created by dispersing particles in a liquid medium, whereby the particles self-align into an ordered array. The particles are fused together by mutual polymerization or by introducing a solvent that swells and fuses the particles together.
In other uses of CCAs, an ordered array is fixed in a matrix and may be used as a colorant when the fixed array diffracts radiation in the visible spectrum. Alternatively, CCAs are fabricated to diffract radiation for use as optical filters, optical switches, and optical limiters. While these CCAs use constant inter-particle spacing, a CCA may also function as a sensor when the inter-particle spacing varies in response to stimuli.
More recently, CCAs have been used to exhibit images as described in U.S. Patent Application Publication No. 2009/0155545, incorporated herein by reference. An image is produced by exposing one portion of a CCA to radiation and altering another portion of the CCA, such that the first portion and the other portion diffract radiation at different wavelengths, rendering the image detectable. The first portion may correspond to the image with the second serving as a background, or vice versa, wherein the first portion is a background to an image produced in the second portion.